Add the data model for structures and prevent them from being embedded in most actors.

module/documents/Item/Handler.mjs

@@ -1,11 +1,13 @@
 import AspectItem from "./Aspect.mjs";
 import SpellItem from "./Spell.mjs";
+import StructureItem from "./Structure.mjs";
 
 /** @extends {Item} */
 export class ItemHandler extends Item {
 	proxyTargets = {
 		aspect: AspectItem,
-		spell: SpellItem
+		spell: SpellItem,
+		structure: StructureItem,
 	};
 
 	constructor(data, ctx) {